8

Few authors* have expressed their opi-nion on the subject of syenite, porphyry,hovnblend rock, greenstone, serpentine, pri-mitive and transition limestone, siliceousslate, greywacke; but the stratification ofthese and other substances is no less am-biguous than that of granite. M. de Luc,for a long time denied, that any of the pri-mitive, or as he calls'them, primordial rockswere to be found stratified. This opinionwas afterwards renounced by him b , but stillfound a supporter in la Metherie. c

The term flotz-rocks was originally, I be-lieve, employed upon the supposition thatin them only was stratification observable,a supposition which is doubly erroneous, astratiform structure, in whatever sense thatphrase is used, being neither peculiar toflotz-rocks nor essential to them. Trap, asubstance which derived its name from thecircumstance of its occurring in successivesteps, or terraces, piled one above another,

* Jameson’s Geol. and J. des M. vol. xxvi. p. 173.b Journ. de Physique, vol. xxxviii. p. 372.c Thcorie de la Terre, vol. iv. p. 352.